Synthesis And Application Of Noble Metal Nanoclusters

Noble metal nanoclusters have attracted increasing attention in recent yearsbecause they exhibit optical and chemical properties which are dramatically differentfrom larger noble metal nanoparticles. Among noble metal nanoclusters (NCs), Au andAg NCs are the most popular ones, mainly owning to their strong fluorescenceproperty, stability, and biocompatibility for applications in optical sensing, imaging,catalysis and single molecular spectroscopy. In this paper, we focused on the synthesisand application of fluorescent Au and Ag NCs based on different templates, andsummarized as follows:1. A novel resonance light scattering (RLS) assay for the sensitive and selectivedetection of iodide ions was developed based on histidine-stabilized gold nanoclusters(His-AuNCs). Iodide ions can cause the fusion and aggregation of His-AuNCs andsignificantly enhance their RLS signal, which is dependent on the iodide concentrationand can be used for the assay of iodide. The RLS signal enhancement was found to beproportional to the iodide concentration over the range of10nM-8.0μM, and thedetection limit of this iodide assay was calculated to be as low as1.8nM at asignal-to-noise ratio of3. Moreover, this RLS signal “turn on” assaying method ishighly selective for iodide, and it can be used for the detection of iodide ions in realwater samples.2. We describe a simple ‘‘top-down’’ approach, employing polyethylenimine (PEI)as a reducing, etching and capping reagent, to the synthesis of fluorescent goldnanoclusters (AuNCs). The fluorescence spectra, UV-vis spectra and high resolutiontransmission electron microscopy (HRTEM) were carried out to characterize theoptical properties and morphologies of PEI-AuNCs. PEI-AuNCs have been developedas a highly sensitive fluorescent pH sensor. Quantitatively, the fluorescence intensity ofPEI-AuNCs exhibits a linear fashion over the pH range of4.56to8.69. Withincreasing pH, the number of charged amine groups decrease and induce theaggregation of AuNCs, which is considered to produce fluorescence quenching ofAuNCs at high pH values. 3. In this study, interactions of dihydrolipoic acid-capped silver nanoclusters(DHLA-AgNCs) with bovine serum albumin (BSA) were investigated in detail bysteady-state fluorescence, ultraviolet visible (UV-vis) absorption, synchronousfluorescence, and surface-enhanced Raman scattering (SERS) spectroscopy. It wasfound that BSA could bind to the surface of DHLA-AgNCs, with its intrinsicfluorescence quenched by DHLA-AgNCs through a dynamic quenching mechanism.The fluorescence quenching constant was determined using the Stern-Volmer equationand the modified Stern-Volmer equation. Moreover, in the presence of DHLA-AgNCs,BSA exhibited a conformational structure alteration, which was verified by the UV-visabsorption, synchronous fluorescence, and SERS spectra.